Plessy is famous for having constitutionalized the concept of "separate but equal" accommodations for blacks, a doctrine which legitimized Jim Crow and led to the civil rights strife of the mid twentieth century.

The dispute arose over a Louisiana statute, typical of the Jim Crow laws being passed at the time, which required railroads to provide "separate but equal" accommodations for blacks and whites, and required travelers to use only those cars set aside for their race. A New Orleans coalition of creoles and blacks decided to test the constitutionality of the law.

Plessy agreed to create the conditions for the case. One eighth black, he was considered legally black, though appearing white. In buying a railroad ticket, he made sure that the conductor was aware of his mixed race. When he seated himself on a white car and refused to move, he was arrested.

Plessy charged that his rights under the Thirteenth and Fourteenth Amendments were violated by the law and, when the Louisiana courts refused to acknowledge his claims, he appealed to the Supreme Court.

In his majority opinion, Justice Henry B. Brown held that the Thirteenth Amendment only prohibited acts which threatened a return to slavery, which Louisiana's law clearly did not. He further stated that the Fourteenth Amendment's guarantee of equal protection of the laws did not apply, since the Louisiana statute did not inherently treat blacks as inferior -- that the feelings of inferiority came from blacks' perception of the law. He also expressed the futility of trying to create laws that flowed against the long-held customs and sentiments of the people.

To insure that his position met with popular support, Justice Brown equated the separation of races on railway cars with the similar separation in the state educational system -- the latter being a particularly strongly held sentiment of the white majority.

In his lone dissent, Justice John Marshall Harlan rejected the notion that the Thirteenth Amendment was restricted to slavery itself, instead proposing, with a vagueness usually eschewed by the Court, that it also addressed the "badge[s] of servitude". In an oft-repeated phrase -- which actually came from one of Plessy's attorneys -- Justice Harlan stated that the "Constitution is color-blind, and neither knows nor tolerates classes among citizens."

In expanding the constitutionality of enforced segregation to include a field so broad and delicate as education, the Court fairly well assured the civil rights actions of a half century later. As much as anything else, the doctrine of separate but equal was blown away by the fact that Jim Crow's separate accommodations never approached equal.